Hydraulic jack with back pressure safety check



June 14, 1966 A. G. LONDON 3,255,587

HYDRAULIC JACK WITH BACK PRESSURE SAFETY CHECK Filed June 27, 1962 LOAD I INVENTOR AA WW 6. L O/VDO/V United States Patent 3,255,587 HYDRAULIC JACK WITH BACK PRESSURE SAFETY CHECK Alvan G. London, Wauwatosa, Wis., assignor to Applied Power Industries, Inc., Milwaukee, Wis., a corporation of Wisconsin Filed June 27, 1962, Ser. No. 205,575 3 Claims. (Cl. 60-52) This invention relates to a safety improvement in hydraulic systems for moving a reactive or live load, and relates specifically to an improvement for preventing the fall of a raised load in the event there is a pressure loss in the fluid transmission system. The prior art has taught safety mechanisms which include pilot lines for the sensing and sending of pressure loss intelligence to a safety mechanism. However due to their costly nature, and due to the fact that, if the pilot lines were plugged or restricted along their lengths, performance became erratic or inoperative, and such safety devices did not fill the requirement of the art. Therefore, a principal objective of the present invention is to provide an inexpensive, reliable safety device to prevent personal injury and property damage from such mechanisms.

More particularly, the invention provides safety checks built into the pressure cylinder itself, which eliminate pilot lines and provides apparatus for using a back pressure princple for activating the safety mechanism.

A further objective of the invention is to provide a system which relies on only one conduit between the pumping station and the load lifting jack, and further provides a relatively free flow of fluid from the station to the jack, but includes a controlled, restricted flow.

from the jack to the pumping station.

A further objective of the invention is to provide a reliable safety device having steps of operation which are I telligence rather than fluid flow.

These and other objectives and advantages of the invention will be more fully understood upon a reading of the following specifications taken in view of the attached drawings wherein:

FIGURE 1 is a schematic-diagrammatic view of a cylinder-safety check-hand pump combination; and

FIGURE 2 is a sectional view of the back pressure safety assembly.

Referring now to the drawings more in detail, wherein like numerals indicate like elements, a load lifting hydraulic systemis indicated by the numeral 6. The system is basically comprised of a load lifting cylinder or jack 8, a back pressure operated safety check housing 10, and a hand pump or the like 12. In the embodiment described, the housing forms the bottom of jack 8.

In the present invention, a single fluid conduit 14 of a selected length communicates the pump assembly 12 to the interior of the housing. Within the interior of the pumping station, a first branch line or passageway 13 connects conduit 14 to tank. Along the length of branch line 13, there is a pressure release valve (diagrammatically shown) 19 which may be of a standard needle type construction. A second branch or passageway connects the fluid reservoir or tank (as indicated by the letter T) to the intake of the pumping cylinder18.

The interior of the safety housing 10 is disclosed in FIGURE 2. The housing is formed with a plurality of access channels including an inlet bore 20 which receives the conduit 14, and an outlet bore 21 leading directly to the pressure end of the lifting jack. The housing is also formed with two check ball receiving bores .22 and 29, and a piston bore 24.

Within bore 22 there is a checkball 32 biased toward its seat 33 by a compression spring 34. The spring is positioned by a threaded plug 35 having an orifice 37 therethrough. Within bore 29 there is a check ball biased toward its seat 31 via a compression spring 27. A suitable plug member 28' is threadably received within the outer end of bore 29 and provides a base upon which the spring may rest. A cross bore 39 communicates the lower ends of bores 22 and 29. A threaded plug member 22' is provided to seal bore 22 and a threaded plug 39' is provided to seal bore 39.

Passageway 20 is placed in communication with the upper end of bore 24 and the inlet sides of bores 29 and 22 by a pressure sensing passageway 38.

The bore 24 is comprised of a stem receiving section 40, a counter bore 42, and an outer threaded section 44. 'A shoulder 46 is formed between section 40 and counter bore 42, and section 40 is terminated about its lower end by an annular flange 41. The upper end of bore 24 is sealed by a conventional cap screw and seal assembly 48. A floating inverted U-shaped piston 50 is slidably received in counter bore 42. Its upper limit of movement is terminated by cap 48 and its lower limit is terminated by shoulder 46. Receivable within ,the inverted, piston is a valve stem 54 having an annular, outwardly, extending flange 56 about its upper surface and an extension 58 of reduced cross-section at its lower end. It will be noted that compression spring 52 is secured between the lower surface of flange 56 and shoulder 46. Springs 52 and 34, therefore, are effective in biasing the stem 58 and piston 50 normally upwardly. Flange 56 is not essential and it should be understood that spring 52 would perform the same function of biasing piston 50 upwardly if it were received between shoulder 46 and the bottom of the counterbore.

The bore 24 is coaxial with bore 22 which permits the extension 58 to remove ball 32 from its seat when in its lower position (as seen in FIG. 2). It will be noted that extension 58 penetrates passageway 38 but is so dimensioned that it does not seriously interfere with fluid flow therethrough.

In operation, pump 12 develops a pressure in fluid line 14 which transmits a pressure into the interior of the housing 10 via aperture 20. As pressure increases, check balls 30 and 32 are forced from their respective seats permitting .relatively free fluid flow through passageway 21 into the pressure side of lift cylinder 8. Concurrent with the increasing pressure, passageway 38 permits pressure to reflect itself on the upper surface of the floating piston, causing the stem 54 and stem extension 58 to engage ball 32 and positively hold it from its seat 33.

When the load is lifted to a desired level, an operator completely opens valve 19 such that line 14 is dumped to tank. As pressure in line -14 falls, the floating stem is biased upwardly by springs 34 and 52 as their strength overcomes the fluid pressure on the upper surface of piston 50. The check balls 30 and 32 are then seated and any displacement of fluid from the'lift cylinder is prevented. At this point the lift cylinder is positively locked at its selected level. When it is desired to lower the load, the valve 19 is closed to interrupt the communication between line 14 and tank, and the operator gives one or two strokes to his pump to develop a pressure in passageway 38 suflicient to overcome the bias of the compression spring 52. Such a pressure causes the stem extension 58 to remove ball 32 from its seat. The valve 19 is then partially opened thus permitting fluid to drain from the lift cylinder via the passageway 21, orifice 37, through inlet 20, line 14, and thence to tank. When valve 19 is only partially opened, the pressure within the system remains sufliciently high to maintain the stem extension 58 in position for unseating ball 32. In other words the pressure in lines 20 and 38 is maintained sufliciently high due to the restricted flow caused by valve 19 to maintain ball 32 away from its seat 33.

It can be seen that any loss of pressure remote from housing 10 will be reflected in passageway 38, causing the load to be positively locked at its existing height. Only through the application of additional pressure in passageway 38 can fluid be drained from cylinder 8. It should be noted that the fluid leaving the rod end of the cylinder must all pass through the orifice 37. In the event it is desired to drain the cylinder at different rates, it is an easy matter to substitute a plug having either a greater or lesser orifice diameter. Due to the fact that bore 21 is immediately adjacent the cylinder, it is extremely unlikely that a faulty condition would develop therein. This is true even though some environments may call for the housing to be displaced slightly from the cylinder and the connection accomplished by a short steel conduit or a suitable fitting.

In a general manner, while there has been disclosed an effective and efiicient embodiment of the invention, it should be well understood that the invention is not limited to such an embodiment, as there might be changes made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

I claim:

1. A safety circuit for a hydraulic system comprising in combination, a hydraulic pump having an inlet in fluid communication with a reservoir and an outlet, a first fluid connection between said outlet and said reservoir, and a second fluid connection between said reservoir and the intake of said pump, a release valve for opening, partially opening or closing said first fluid connection, a lift jack operable by said pump, a hydraulic back pressure safety housing forming an end wall of said jack, a conduit in fluid communication with said first fluid connection, said housing having a first bore receiving said conduit and a second bore in communication with said jack, first and second passageways between said bores, a check ball in said first passageway normally blocking fluid flow therethrough from said second bore to said first bore and permitting relatively free flow from said first bore to said second bore, a one way check valve and a restriction orifice in said second passageway, and a plunger to open said check valve when fluid is to be drained from said jack through said release valve causing all of said fluid to exhaust through said orifice.

2. A safety circuit for a hydraulic system comprising in combination, a hydraulic pump having an inlet in fluid communication with a reservoir and an outlet, a first fluid connection between said outlet and said reservoir, a release valve having a first position for opening, a second position for partially opening and a third position for closing said first fluid connection, an expansion cylinder operable by said pump, a bottom housing enclosing said cylinder, a conduit in fluid communication with said outlet, said housing having a first bore receiving said conduit and a second bore in communication with said cylinder, passageway means between said bores, first and second one-Way check valves in parallel arrangement in said passageway means normally blocking flow from said second bore to said first bore and normally permitting fluid flow from said first bore to said second bore, a piston reciprocal in said housing having a first position which opens said first check valve, and a second retracted position, and means causing said piston to move to said first position when said release valve is in said second position.

3. A safety circuit for a hydraulic system comprising in combination, a hydraulic pump having an inlet in fluid communication with a reservoir and an outlet, a first fluid connection between said outlet and said reservoir, and a second fluid connection between said reservoir and said pump, a release valve for opening, partially opening or closing said first fluid connection, an expansion cylinder operable by said pump, a hydraulic back pressure safety housing enclosing one end of said cylinder, a conduit in fluid communication with said first fluid connection, said housing having a first bore receiving said conduit and a second bore in direct communication with the interior of said cylinder, passageway means communicating said bores, valve means in said passageway means having a first position normally blocking fluid flow from said second bore to said first bore and permitting relatively free fluid flow in said passageway means from said first bore to said second bore, a third bore in said housing communicating with said passageway means, a stem member slidably received in said third bore having one end movable to a retracted position and to an extended position when in said extended position said stem causing said valve means to move from said first position to a second position permitting fiuid flow between said second bore and said first bore, and fourth bore means communicating the pressure in said first bore to the other end of said stem.

References Cited by the Examiner UNITED STATES PATENTS 974,988 11/1910 Northam 52 2,286,880 6/1942 Traut 91-446 X 2,603,235 7/1952 Kirkham 91443 X 2,618,929 11/1952 Bidin 6052 2,868,174 1/1959 Shutt 91-443 2,954,800 10/1960 Searles et al 9l446 X JULIUS E. WEST, Primary Examiner. 

1. A SAFTEY CIRCUIT FOR A HYDRAULIC SYSTEM COMPRISING IN COMBINATION, A HYDRAULIC PUMP HAVING AN INLET IN FLUID COMMUNICATION WITH A RESERVOIR AND AN OUTLET, A FIRST FLUID CONNECTION BETWEEN SAID OUTLET AND SAID RESERVOIR, AND A SECOND FLUID CONNECTION BETWEEN SAID RESERVOIR AND THE INTAKE OF SAID PUMP, A RELEASE VALVE FOR OPENING, PARTIALLY OPENING OR CLOSING SIAD FIRST FLUID CONNECTION, A LIFT JACK OPERABLE BY SAID PUMP, A HYDRAULIC BACK PRESSURE SAFETY HOUSING FORMING AN END WALL OF SAID JACK, A CONDUIT IN FLUID COMMUNICATION WITH SAID FIRST FLUID CONNECTION, SAID HOUSING HAVING A FIRST BORE RECEIVING SAID CONDUIT AND A SECOND BORE IN COMMUNICATION WITH SAID JACK, FIRST AND SECOND PASSAGEWAYS BETWEEN SAID BORES, A CHECK BALL IN SAID FIRST PASSAGEWAY NORMALLY BLOCKING FLUID FLOW THERETHROUGH FROM SAID SECOND BORE TO SAID FIRST BORE AND PERMITTING RELATIVELY FREE FLOW FROM SAID FIRST BORE TO SAID SECOND BORE, A ONE WAY CHECK VALVE AND A RESTRICTION 